1. Field of the Invention
The present invention relates to an optical pick-up actuator for a tilt compensation servo associated with high-density disks.
2. Description of the Related Art
With the development of disk media capable of optically recording information and reproducing the recorded information, diverse products have been developed in association with optical pick-up devices adapted to read information recorded on disks.
In an optical recording/reproducing system for optically recording and reproducing information, an object lens driving unit configured to allow an optical spot to follow the surface vibrations and eccentricity of a disk is used, along with the optical system of a pick-up device, in order to achieve desired focusing and tracking operations.
This object lens driving unit is called an “optical pick-up actuator”. The current tendency of designs and developments associated with such an optical pick-up actuator is toward those suitable for high-density disks.
Generally, such an optical pick-up actuator includes a lens holder adapted to hold an object lens. The lens holder should be configured to move upward, downward, left and right directions, for desired focusing and tracking operations of the object lens. This driving unit also includes coils arranged in a magnetic space defined by a magnet and a magnetic body, so that it utilizes a Lorentz force according to the Fleming's left-hand law.
FIGS. 1a to 1c are schematic views respectively illustrating the configuration of a conventional optical pick-up actuator.
Referring to FIGS. 1a to 1c, the conventional optical pick-up actuator includes a lens holder 102 adapted to hold an object lens 101, magnets 103, yokes 106, a focusing coil 108, a tracking coil 109, fixed printed circuit boards (PCBs) 110, a plurality of wire springs 111, and a frame 112.
In the optical pick-up actuator illustrated in FIG. 1, the lens holder 102 mounted with the object lens 101 is movable in accordance with the function of the wire springs 111. The object lens 101 is centrally attached to the lens holder 102. The focusing coil 108 is wound around the lens holder 102. The tracking coil 109, which is wound in a rectangular form, is attached to the upper surface of the focusing coil 108. The fixed PCBs 110 are fixedly mounted to opposite side surfaces of the lens holder 102, respectively The yokes 106 are symmetrically arranged at opposite vertical sides of the object lens 101, respectively. The magnets 103 are arranged to apply magnetic flux to the tracking coil 109 and focusing coil 108, thereby causing the tracking coil 109 and focusing coil 108 to generate electromagnetic forces, respectively.
The yokes 106 are installed to be integral with a pick-up base, using an integral attachment means.
The frame 112 is arranged at one edge of the optical pick-up actuator. A main PCB not shown is fixedly mounted to the frame 112 by means of set screws. Each of the wire springs 111 is coupled to the frame 112 at one end thereof. Typically, four wire springs 111 are coupled to the frame 112. The other end of each wire spring 111, which is coupled to the frame 112 at one end thereof, is connected to an associated one of the fixed PCBs 110 attached to the lens holder 102. In accordance with such an arrangement, the lens holder 102 is maintained in a suspended state by the wire springs 111.
As shown in FIGS. 1b and 1c, the conventional optical pick-up actuator having the above mentioned configuration is a biaxially-driving optical pick-up actuator. That is, the coils of this optical pick-up actuator, that is, the focusing coil 108 and tracking coil 109, are arranged in such a fashion that they face the magnets 103, so that the focusing coil 108 carries out upward and downward driving (focusing) operations whereas the tracking coil 109 carries out left and right driving (tracking) operations.
Due to a reduced tilt margin resulting from an application to high-density disks and a limited tilt tolerance allowed in the assembling work, however, it is required to use a servo for compensating a tilt occurring during the driving operation of the actuator, in addition to the configurations required for the tracking and focusing operations.
FIG. 2 schematically illustrates the configuration of a conventional quadaxially-driving optical pick-up actuator.
Referring to FIG. 2, the conventional quadaxially-driving optical pick-up actuator has a driving configuration having a desired degree of freedom in radial and tangential direction, in addition to a desired degree of freedom in the focusing and tracking driving directions.
This driving configuration will now be described in detail. In the quadaxially-driving optical pick-up actuator, two coils are symmetrically arranged at a fixed body, as in the case of FIG. 1a. Two additional coils 204 and 205 are symmetrically arranged in order to achieve radial and tangential driving operations for a tilt compensation. A pair of magnets 203 are attached to a moving body while facing the coils 204 and 205. In accordance with such arrangements, a lens holder 202 attached with the magnets 203 can be driven while having four degrees of freedom. This optical pick-up actuator conducts a servo operation, based on error signals respectively indicative of tilt variations of the lens and disk optically detected.
Although the connection of the tracking and focusing coils to a power source is achieved by the four wire springs adapted to provide a desire support in the configuration of FIG. 1a, an additional power connection means is required to connect the tilting coils in the case of FIG. 2, in addition to the four wire springs used for the tracking and focusing coils. As a result, the configuration of FIG. 2 is complex
The additional magnets attached to the lens holder are considerably heavier than the lens holder. For this reason, a considerable increase in the mass of the moving body occurs, thereby resulting in a degradation in sensitivity.
Furthermore, where the above-mentioned optical pick-up actuator is applied to high-density disks, the frequency characteristics for focusing and tracking servos are undesirably shifted toward a higher frequency band because of an increased data processing rate and a reduced high-pass surface vibration limit.